In an image-forming process by means of an electrophotographic system, an electrostatic latent image is formed on a photoconductive material made of an inorganic or organic material, and the latent image is developed by a toner, then transferred and fixed on a paper sheet or plastic film to obtain a visible image. The photoconductive material may be positively electrifiable or negatively electrifiable depending upon its construction. When a printed portion is remained as an electrostatic latent image by exposure, development is conducted by means of an oppositely electrifiable toner. On the other hand, when a printed portion is destatisized for reversal development, development is conducted by means of an equally electrifiable toner.
A toner is composed of a binder resin, a coloring agent and other additives. However, in order to impart desired tribocharge properties (such as desired charge up speed, tribocharge level and tribocharge level stability), stability with time and environmental stability, it is common to use a charge-control agent. The properties of the toner will be substantially affected by this charge-control agent. When a positively electrifiable photoconductive material is used for development by an oppositely electrifiable toner, or when a negatively electrifiable photoconductive material is used for reversal development, a negatively electrifiable toner is used. In such a case, a negatively electrifiable charge-control agent is added. Further, in a case of a color toner for which the market is expected to expand in future, it is necessary and indispensable to use a pale-colored or preferably colorless charge-control agent which does not affect the color of the toner. Such pale-colored or colorless charge-control agents may, for example, be metal complex salt compounds of salicylic acid derivatives (e.g. JP-B-55-42752, JP-A-61-69073 and JP-A-61-221756), aromatic dicarboxylic acid metal salt compounds (e.g. JP-A-57-111541), metal complex salt compounds of anthranilic acid derivatives (e.g. JP-A-62-94856) and organic boron compounds (e.g. U.S. Pat. No. 4,767,688 and JP-A-1-306861). However, these charge-control agents have various drawbacks such that some of them are chromium compounds which are feared to be detrimental to environmental safety which is expected to be viewed as increasingly important, some of them are compounds which can not be made adequately colorless or pale-colored as required for toners, some of them have inadequate electrifying effects or provide oppositely electrifiable toners, or some of them are poor in dispersibility or chemical stability as compounds themselves. Thus, none of them has fully satisfactory properties as a charge-control agent. Accordingly, it is an object of the present invention to provide an electrophotographic toner which is excellent in the tribocharge property and capable of constantly and stably presenting an image of high image quality, characterized by using a specific combination of a binder resin and a compound which is colorless or pale-colored and excellent in environmental safety and has a high stability as a compound and which is useful as a charge-control agent for the electrophotographic toner and excellent in the dispersibility in the binder resin.